We propose the overarching hypothesis that liver non-parenchymal, antigen-presenting cells (ARC) serve as key regulators of hepatic-based inflammatory/immune responses. The proposed Program Project will bring together the collective expertise of a highly-experienced and interactive, interdisciplinary group of investigators, established in the study of APC function, hepatic ischemia-reperfusion (I/R) injury, liver immunobiology, and transplantation. Complementary skills and expertise of the team will be melded to elucidate mechanisms and resolve apparent paradoxes underlying the distinctive role of specific liver APC populations in innate immunity and regulation of adaptive immunity. There is strong potential for development of novel therapeutic strategies to improve liver allograft outcome. The Program's goal is to understand, through collaborative interaction, mechanisms underlying the role of specific liver APC, that generally dampen systemic immune responses to gut-derived Ags, in regulation of liver injury and hepatic immunity relevant to transplant outcome. Project 1 will focus on mechanisms by which the hepatocyte-derived transcription factor interferon regulatory factor-1 (IRF-1) and hepatocyte injury overwhelm the natural tendency of the liver to suppress inflammatory/immune responses after liver I/R injury. Aim I: will identify the signaling pathways and role of liver APC (DCs, Kupffer cells and stellate cells) in regulation of hepatic IRF-1 expression;Aim II: will elucidate the mechanisms of hepatic IRF-1-mediated liver injury;Aim III: will determine whether IRF-1 blockade can ameliorate liver transplant I/R injury. Project 2 will focus on mechanisms that regulate liver DC maturation and function and determine their role in the initiation and regulation of T cell function and liver transplant outcome. Aim I: will elucidate the role of inducible regulators of Toll-like receptor (TLR) signaling in endotoxin tolerance in liver DC;Aim II: will ascertain the contribution of specific pro- and anti-inflammatory cytokines, expressed in the steady-state and during I/R injury, to endotoxin tolerance in liver DC. Aim III: will establish the contribution of donor DC, TLR4 and negative regulators of TLR signaling in liver DC to T cell responses following experimental liver transplantation;Aim IV: will determine the maturation status of hepatic DC, including expression of negative regulators of maturation, in relation to human liver transplant outcome. Project 3 will define mechanisms by which hepatic stellate cells participate in I/R injury and regulate the function of DC and T lymphocytes in relation to liver transplant outcome. Aim I: will ascertain the influence of hepatic stellate cells on IRF-1 and liver I/R injury;Aim II: will determine mechanisms underlying the regulation of DC and T lymphocyte function by hepatic stellate cells;Aim III: will ascertain the role of hepatic stellate cells in the regulation of liver allograft outcome. These three Projects will be supported by an Administrative Core (Core A), that will co-ordinate programatic functions, an Imaging and Tissue Pathology Core (Core B). and a small animal Transplantation Surgery Core (Core C).